package main

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"log"
	"log/slog"
	"os"
	"time"
	_ "time/tzdata"

	mqtt "github.com/eclipse/paho.mqtt.golang"
	"github.com/joho/godotenv"
	_ "github.com/lib/pq"
)

// Payload struct
//
// All metrics are stored in PostgreSQL as INT and not NUMERIC or FLOAT to optimise their storage size.
//
// Dt1, Dt2, Rt1, Rt2 and G are cumulative meter readings.
// By making them pointers to int, they can be set to 'nil' when the reading has not changed.
// This way, they are logged as NULL in the database when no change has happened, saving storage capacity.
// As an added benefit, this also make data retrieval, visualisation and analysis more light-weight.
//
// Gas consumption is updated once per minute.
// Not saving intermittent values theoretically saves 4 bytes per value.
//   Storage for non-NULL values every second:
//     86,400 entries/day×4 bytes/entry=345,600 bytes/day86,400entries/day×4bytes/entry=345,600bytes/day
//   Storage for non-NULL values every minute:
//     1,440 entries/day×4 bytes/entry=5,760 bytes/day1,440entries/day×4bytes/entry=5,760bytes/day
//   Storage savings:
//     345,600 bytes/day−5,760 bytes/day=339,840 bytes/day345,600bytes/day−5,760bytes/day=339,840bytes/day
//     (about 331.5 KB / day or 9.72 MB / month)
//   In practice, savings will be even higher when gas is not being consumed continuously.
//
// When Tariff 1 is active, Tariff 2 isn't.
// When energy is being imported, it is not being returned.
//   Therefore, only updating their values on-change should save at least 75% storage capacity requirements
//   An average month has 2 629 743.83 seconds.
//   This saves at least:
//     2,629,743.83 seconds * 4 bytes = 10,518,975.32 bytes = 10,518.98 kB = 10.52 MB
//   This applies both to Dt1 and Dt2 as well as Rt1 and Rt2, only one is recorded at a time.
//     10.52 * 3 = 31.56 MB.
// In addition, many meters only update these metrics once every 10 seconds,
// meaning even more storage capacity is saved:
// 10.52 / 10 * 9 = 9,468 MB.

type Payload struct {
	T   string `json:"t"`   // Timestamp
	Dt1 *int   `json:"dt1"` // Delivered / imported meter reading tariff 1 (kWh)
	Dt2 *int   `json:"dt2"` // Delivered / imported tariff 2 (kWh)
	Rt1 *int   `json:"rt1"` // Returned / exported tariff 1 (kWh)
	Rt2 *int   `json:"rt2"` // Returned / exported tariff 2 (kWh)
	D   int    `json:"d"`   // Delivering / importing (W)
	R   int    `json:"r"`   // Returning / exporting (W)
	F   int    `json:"f"`   // Failure (counter)
	Fl  int    `json:"fl"`  // Failure long duration (counter)
	G   *int   `json:"g"`   // Gas meter reading (l)
	V1  int    `json:"v1"`  // Voltage L1 (V)
	V2  int    `json:"v2"`  // Voltage L2 (V)
	V3  int    `json:"v3"`  // Voltage L3 (V)
	C1  int    `json:"c1"`  // Current L1 (A)
	C2  int    `json:"c2"`  // Current L2 (A)
	C3  int    `json:"c3"`  // Current L3 (A)
	D1  int    `json:"d1"`  // Delivering / importing L1 (W)
	D2  int    `json:"d2"`  // Delivering / importing L2 (W)
	D3  int    `json:"d3"`  // Delivering / importing L3 (W)
	R1  int    `json:"r1"`  // Returning / exporting L1 (W)
	R2  int    `json:"r2"`  // Returning / exporting L2 (W)
	R3  int    `json:"r3"`  // Returning / exporting L3 (W)
}

var db *sql.DB
var logger = slog.New(slog.NewJSONHandler(os.Stdout, nil))

func main() {
	slog.SetDefault(logger)

	// Load environment variables from .env file if it exists
	if err := godotenv.Load(); err != nil {
		logger.Info("No .env file found or error loading .env file (ignore this message when using container)", "error", err)
	}

	// Connect to PostgreSQL
	pgConnStr := os.Getenv("PG_DB")
	if err := connectToPostgreSQL(pgConnStr); err != nil {
		log.Fatal("Error connecting to PostgreSQL", "error", err)
	}

	// Initialize MQTT options
	opts := mqtt.NewClientOptions()
	opts.AddBroker(os.Getenv("MQTT_BROKER"))
	opts.SetUsername(os.Getenv("MQTT_USERNAME"))
	opts.SetPassword(os.Getenv("MQTT_PASSWORD"))
	opts.SetAutoReconnect(true)
	opts.SetConnectionLostHandler(func(client mqtt.Client, err error) {
		logger.Error("Connection lost", "error", err)
	})
	opts.SetOnConnectHandler(func(client mqtt.Client) {
		topic := os.Getenv("MQTT_TOPIC")
		logger.Info("Connected to MQTT broker, subscribing to topic...", "topic", topic)
		if token := client.Subscribe(topic, 0, mqttMessageHandler); token.Wait() && token.Error() != nil {
			logger.Error("Error subscribing to MQTT topic", "topic", topic, "error", token.Error())
		}
	})

	// Connect to MQTT broker
	client := mqtt.NewClient(opts)
	if token := client.Connect(); token.Wait() && token.Error() != nil {
		log.Fatal(token.Error())
	}

	// Keep the program running
	select {}
}

var prevDt1, prevDt2, prevRt1, prevRt2, prevG int

func updateFieldIfChanged(currentValue *int, previousValue *int) (*int, bool) {
	if currentValue != nil && *currentValue == *previousValue {
		return nil, false // No change
	} else if currentValue != nil {
		*previousValue = *currentValue // Update the previous value to the current one
		return currentValue, true      // Change occurred
	}
	return currentValue, false // Return the original value if it's nil, indicating no change
}

// safeDerefInt handles potential nil pointers to avoid a runtime panic
// log messages will display the actual integer values if the pointers are not nil,
// or "nil" if the pointers are nil.
func safeDerefInt(ptr *int) string {
	if ptr != nil {
		return fmt.Sprintf("%d", *ptr) // Dereference the pointer to get the value
	}
	return "nil" // Return a string indicating the value is nil
}

func mqttMessageHandler(client mqtt.Client, msg mqtt.Message) {
	// Parse JSON payload
	var payload Payload
	err := json.Unmarshal(msg.Payload(), &payload)
	if err != nil {
		logger.Error("Error parsing MQTT payload", "error", err)
		return
	}

	// Parse timestamp to time.Time
	timestamp, err := parseTimestamp(payload.T)
	if err != nil {
		logger.Error("Error parsing timestamp", "error", err)
		return
	}

	var changed bool // Flag to track if any value changed

	// Update each field, directly updating `changed` if any change is detected
	var tempChanged bool // Used to capture the change status for each field
	payload.Dt1, tempChanged = updateFieldIfChanged(payload.Dt1, &prevDt1)
	changed = changed || tempChanged

	payload.Dt2, tempChanged = updateFieldIfChanged(payload.Dt2, &prevDt2)
	changed = changed || tempChanged

	payload.Rt1, tempChanged = updateFieldIfChanged(payload.Rt1, &prevRt1)
	changed = changed || tempChanged

	payload.Rt2, tempChanged = updateFieldIfChanged(payload.Rt2, &prevRt2)
	changed = changed || tempChanged

	payload.G, tempChanged = updateFieldIfChanged(payload.G, &prevG)
	changed = changed || tempChanged

	// If any value has changed, log all the relevant values
	if changed {
		logger.Debug("Values changed",
			"dt1", safeDerefInt(payload.Dt1),
			"dt2", safeDerefInt(payload.Dt2),
			"rt1", safeDerefInt(payload.Rt1),
			"rt2", safeDerefInt(payload.Rt2),
			"g", safeDerefInt(payload.G))
	}
	// Insert data into PostgreSQL
	err = insertData(timestamp, payload)
	if err != nil {
		logger.Error("Error inserting data into PostgreSQL", "error", err)
	}
}

func parseTimestamp(t string) (time.Time, error) {

	// Extract values from timestamp string
	year, month, day := 2000+int(t[0]-'0')*10+int(t[1]-'0'), time.Month(int(t[2]-'0')*10+int(t[3]-'0')), int(t[4]-'0')*10+int(t[5]-'0')
	hour, min, sec := int(t[6]-'0')*10+int(t[7]-'0'), int(t[8]-'0')*10+int(t[9]-'0'), int(t[10]-'0')*10+int(t[11]-'0')

	// Load location for "Europe/Amsterdam" time zone
	loc, err := time.LoadLocation("Europe/Amsterdam")
	if err != nil {
		return time.Time{}, err
	}

	// Create and return the timestamp
	return time.Date(year, month, day, hour, min, sec, 0, loc), nil

}

func insertData(timestamp time.Time, payload Payload) error {
	// Prepare SQL statement
	stmt := `
		INSERT INTO p1 (
			timestamp, delivered_tariff1, delivered_tariff2, returned_tariff1, returned_tariff2,
			delivery_all, returning_all, failures, long_failures, gas,
			voltage_l1, voltage_l2, voltage_l3,
			current_l1, current_l2, current_l3,
			delivery_l1, delivery_l2, delivery_l3,
			returning_l1, returning_l2, returning_l3
		) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, $18, $19, $20, $21, $22)
	`
	_, err := db.Exec(
		stmt,
		timestamp,
		payload.Dt1, payload.Dt2,
		payload.Rt1, payload.Rt2,
		payload.D, payload.R,
		payload.F, payload.Fl,
		payload.G,
		payload.V1, payload.V2, payload.V3,
		payload.C1, payload.C2, payload.C3,
		payload.D1, payload.D2, payload.D3,
		payload.R1, payload.R2, payload.R3,
	)
	return err
}

func connectToPostgreSQL(pgConnStr string) error {
	// Connect to PostgreSQL
	var err error
	for {
		db, err = sql.Open("postgres", pgConnStr)
		if err == nil {
			break // Successfully connected
		}

		logger.Error("Error connecting to PostgreSQL", "error", err)
		time.Sleep(5 * time.Second) // Retry after 5 seconds
	}

	// Enable TimescaleDB
	_, err = db.Exec(`
		CREATE EXTENSION IF NOT EXISTS timescaledb;
	`)
	if err != nil {
		log.Fatal("Error creating TimescaleDB extension:", err)
	}

	// Create table if not exists
	_, err = db.Exec(`
		CREATE TABLE IF NOT EXISTS p1 (
			timestamp TIMESTAMPTZ,
			delivered_tariff1 INT,
			delivered_tariff2 INT,
			returned_tariff1 INT,
			returned_tariff2 INT,
			delivery_all INT,
			returning_all INT,
			failures INT,
			long_failures INT,
			gas INT,
			voltage_l1 INT,
			voltage_l2 INT,
			voltage_l3 INT,
			current_l1 INT,
			current_l2 INT,
			current_l3 INT,
			delivery_l1 INT,
			delivery_l2 INT,
			delivery_l3 INT,
			returning_l1 INT,
			returning_l2 INT,
			returning_l3 INT
			);
		SELECT create_hypertable('p1', 'timestamp', if_not_exists => TRUE);
	`)
	if err != nil {
		log.Fatal("Error creating table:", err)
	}

	return nil
}